Neutron-scattering studies of phonons in disordered cubic zirconia at elevated temperatures

Inelastic-neutron-scattering studies of cubic zirconia at elevated temperatures (300–1700 K) showed well-defined LA and TA phonons but no optical-phonon branches were observed, confirming earlier reported reduced Raman scattering data. The LA and TA phonons were observed to broaden with a $q^2$ dependence. The elastic constants $C_{11}$, $C_{12}$, and $C_{44}$ were derived from the dispersion data at room temperature and at elevated temperatures. The frequency distribution of one phonon density of states was generated from the dispersion relation and was found to be in reasonable agreement with the observed Raman spectrum. Also diffuse-elastic-scattering measurements were taken and showed broad intensity peaks in reciprocal space. The scattering and the phonon linewidths showed little temperature dependence; intrinsic defects and anharmonicity dominate the damping mechanism. The unobserved optical branches were obtained by the best fit to the experimentally determined acoustic branches, based upon a rigid-ion-model calculation. Static deformations of the oxygen sublattice due to oxygen vacancies are mainly responsible for the data observed.